From 78195ee848dc846a6415ecb6d6e5329081eb3983 Mon Sep 17 00:00:00 2001
From: Caleb <xxy3429924750@126.com>
Date: Tue, 22 Sep 2026 19:45:41 +0800
Subject: [PATCH] fix(chat): increment temp file suffix correctly

---
 core/chat/message_elements.py  |  2 +-
 tests/test_message_elements.py | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/core/chat/message_elements.py b/core/chat/message_elements.py
index 2abfb32e..9b1146f1 100644
--- a/core/chat/message_elements.py
+++ b/core/chat/message_elements.py
@@ -70,13 +70,13 @@ def _move_no_clobber(source: str, candidate: str) -> Optional[str]:
     numbered candidate. Returns the final path, or None when the move was not
     possible (e.g. filesystems without hard link support).
     """
+    root, ext = os.path.splitext(candidate)
     counter = 1
     while True:
         try:
             os.link(source, candidate)
             break
         except FileExistsError:
-            root, ext = os.path.splitext(candidate)
             candidate = f"{root}_{counter}{ext}"
             counter += 1
         except OSError:
diff --git a/tests/test_message_elements.py b/tests/test_message_elements.py
index c8ce47c5..ca7dac1c 100644
--- a/tests/test_message_elements.py
+++ b/tests/test_message_elements.py
@@ -7,6 +7,7 @@
 from core.chat.message_elements import (
     _build_temp_file_path,
     _infer_mime_from_bytes,
+    _move_no_clobber,
     check_base64,
     ElementType,
     Text,
@@ -25,6 +26,24 @@
 )
 
 
+# ── _move_no_clobber ─────────────────────────────────────────────
+
+def test_move_no_clobber_increments_from_original_candidate(tmp_path):
+    source = tmp_path / "source"
+    source.write_bytes(b"new")
+    candidate = tmp_path / "download.png"
+    candidate.write_bytes(b"original")
+    (tmp_path / "download_1.png").write_bytes(b"first duplicate")
+
+    result = _move_no_clobber(str(source), str(candidate))
+
+    assert result == str(tmp_path / "download_2.png")
+    assert not source.exists()
+    assert candidate.read_bytes() == b"original"
+    assert (tmp_path / "download_1.png").read_bytes() == b"first duplicate"
+    assert (tmp_path / "download_2.png").read_bytes() == b"new"
+
+
 # ── _infer_mime_from_bytes ──────────────────────────────────────────
 
 def test_infer_png():